Development electrode

ABSTRACT

An electrostatic photocopy apparatus uses a liquid developer for developing the electrostatic image on an image bearing sheet. The structure of the developing means utilizes upper and lower electrode means connected to the same electric potential between which the sheet passes in a pool of developer liquid. Both electrodes in a preferred embodiment are in the form of metallic screens, the upper electrode having a mesh size within a range of about 30 mesh to 325 mesh and the lower electrode having a mesh size within a range of about 10 mesh to about 80 mesh. The spacing between the electrodes is in a range between about 1/4 to about 1/16 inch, such close spacing providing improved image contrast without causing any jamming of the sheet as it passes therethrough.

United States Patent Anemaet Mar. 18, 1975 [73] Assignee: DennisonManufacturing (30.,

Framingham, Mass.

[22] Filed: Oct. 16, 1972 [21] Appl. No.: 297,779

[52] 11.8. CI 118/637, 117/37 LE, 118/1316. 23 [51] Int, Cl G03g 13/00[58] Field of Search 1l8/D1G. 23, 637, 638,

[56] References Cited UNITED STATES PATENTS 3,415,223 12/1968 Zweig118/637 3,442,254 5/1969 Akiyama et a1 118/637 3,547,076 12/1970Saklikar 113/D1G. 23 3,577,259 5/1971 Sato et a1. l18/D1G. 23 3,598,0868/1971 Kushima.. 118/612 X 3,605,693 9/1971 Zweig 118/637 3,682,5428/1971 MacKenzie 118/637 X 3,753,393 8/1973 Niesen 118/428 3,799,7913/1974 Kolibas 117/37 LE R27,260 12/1971 MacKenzie ..l18/637 PrimaryExaminer- -Mervin Stein Assistant ExaminerLeo Millstein Attorney, Agent,or Firm-George E. Kersey [57] ABSTRACT An electrostatic photocopyapparatus uses a liquid developer for developing the electrostatic imageon an image bearing sheet. The structure of the developing meansutilizes upper and lower electrode means connected to the same electricpotential between which the sheet passes in a pool of developer liquid.Both electrodes in a preferred embodiment are in the form of metallicscreens, the upper electrode having a mesh size within a range of about30 mesh to 325 mesh and the lower electrode having a mesh size within arange of about 10 mesh to about 80 mesh. The spacing between theelectrodes is in a range between about A to about 1/16 inch, such closespacing providing improved image contrast without causing any jamming ofthe sheet as it passes therethrough.

14 Claims, 2 Drawing Figures DEVELOPMENT ELECTRODE DISCLOSURE OF THEINVENTION Introduction This invention relates generally to electrostaticphotocopying apparatus wherein electrically sensitized paper and liquiddeveloper are utilized and, more particularly, to improved apparatus fordeveloping an image bearing sheet as the sheet is conveyed through thedeveloper station thereof.

1. Background of the Invention 2. Description of the Prior Art In aneffort to improve the developing characteristics of electrostaticphotocopying apparatus, the prior art has found that images may beintensified (i.e., contrast may be improved) by providing upper andlower metal lic electrode members in the developer pool above and belowthe sheet material as it is conveyed therethrough. Such a developerelectrode structure is shown in Reissue U.S. Pat.'No. Re. 27260,reissued on Dec. 28, 1971 to A. K. MacKenzie. As shown therein, theupper metallic member is perforated and the lower one is in the form ofa solid plate having one or more drain holes, both such members beingjuxtaposed opposite the upper and lower surfaces of the sheet materialduring its travel therebetween throughout substantially the width of thesheet.

' In such a structure a liquid developer is supplied through theperforations of the upper member so that a pool thereof is formed by thelower member. It has been found in utilizing such a structure that thesheet material tends to become jammed therein because the bottom, ornon-image, surface thereof tends to adhere to the lower metallicelectrode plate member. In order to overcome such problem the MacKenziepatent teaches the use of a plurality of dielectric guide or rib membersplaced on the upper surface of the lower metallic electrode, the sheet.being permitted to ride over such guides so as not to come into contactwith the lower electrode. Such structure permitted the sheet morereadily to pass between the two electrodes without jamming.

However, even in such a structure it was found that the contrast in thedeveloped image is not always as good as desired, particularly duringhigh speed operation and/or where continuous tone images are beingdeveloped. Although a better image is obtained the closer the spacingbetween the electrodes, such prior art structure, requiring the presenceof dielectric guides, prevents the electrodes from being capable ofplacement sufficiently close to each other to achieve the desiredenhanced image effect.

While an increase in toner concentration in the developer pool in theMacKenzie structure may tend to improve the image intensification, theoperation becomes more expensive and in some applications the increasein toner concentration tends to reach a practical limit wherein anyfurther increase produces no better results.

DESCRIPTION OF THE INVENTION In accordance with the invention describedherein, the upper and lower electrodes in a developer station are formedin such a manner that they can be spaced much closer together than inprior art structures using stationary electrodes so that a relativelynarrow passageway is available therebetween for the sheet as it isconveyed through the developer station. Such close spacing permits theutilization of lower toner concentrations than are required to obtainthe same image contrast in presently known structures. In accordancewith the invention the upper metallic electrode is in the form ofaforaminous metallic material, such as a metallic screen, or othermesh-like structure, while the lower electrode is also in the form of aperforated or meshlike structure, the shape of which is substantiallythe same as that of the upper electrode. It is found that, if bothelectrodes are of a mesh-like structure, such as in the form of metallicscreens, they can be placed very close to each other without causing ajamming of the sheet during its passage through the developer station.In such structure a marked improvement in contrast in the developedimage is achieved. Such a structure eliminates the need for anydielectric guides, or ribs, as are found in the structure of the abovereferenced prior art MacKenzie patent.

A more detailed description of the electrode of the invention isdiscussed with the aid of the accompanying drawing wherein FIG. I. showsa view in cross-section of the development electrode of the invention;and

FIG. 2 shows an enlarged view in cross-section of a portion of thestructure in FIG. 1, taken along the line 2-2 of FIG. 1.

As can be seen in FIG. 1, for the purpose of describing the invention ina preferred embodiment thereof, there is shown a base 10, a tank 11supported on the base, the tank containing a liquid developer 12 up tothe level 13 and having a cover 14 provided with an opening in which asupport 15 is mounted by means of brackets 16. In the support 15 ismounted a tray 17 the bottom of which has a plurality of drainageapertures 18. In the embodiment described, tray 17 can be made of aplastic material or a plastic coated metal, or the like, although italso could be made of metal, if desired. An upper electrode 19 issupported in a frame 20, as by being soldered thereto, which frame is inturn attached to a bracket 21 by end screws 22. The upper electrode 19is a foraminous metal member, in the form, for example, of a metallicscreen.

As a sheet material S having an electrostatic latent image on its uppersurface 23 approaches the tray 17 it is sprayed with a developer througha nozzle 24 which may have a slot or a series of apertures extendingacross the width of the material, the developer being supplied to thenozzle from tank 11 by a suitable pump through conduit 26 and tube 27.The outlet 28 from the tube to the nozzle, which may comprise a slot orseries of apertures, is directed toward a wall 29 in the nozzle for thepurpose of producing turbulence, thereby causing the stream of developerdelivered by the nozzle to be distributed uniformly across the sheet S.Alternatively, the nozzle may be reversed in direction so that theliquid does not strike the paper directly but is generally directedtoward the region ofthe upper electrode so as to form the liquid poolthrough which the sheet passes during its development stage. Developeris pumped into tray 17 faster than it can drain through the bottomapertures thereof so as to maintain the pool in the tray relativelyfull, the excess flowing over the ends of the tray.

The developer in tank 11 is maintained at the level 13 from an invertedbottle 29 having a neck extending through an opening in cover 1d. Thebottle is sealed with foil which, when the bottle is inserted, ispunctured by a tube 30 appropriately mounted thereon, as described inthe aforementioned MacKenzie patent.

A second lower electrode 31 is positioned below upper electrode 19 and,particularly with reference to its portion contiguous to upper electrode19, electrode 31 has substantially the same concave shape and isparallel to the latter electrode. Lower electrode 31 has a large numberof perforations and in a preferred embodiment it may be a foraminous, ormesh-like, metal member, such as a metallic screen, and is supported ina frame bracket 32 as by being soldered thereto at its ends, as shown inFIG. 2.

Bracket 21 is adjustably affixed to'a frame member 33 via screws 34 andslots 35, frame member 33 being in turn appropriately attached to thesupport in any suitable manner (not shown). Bracket 32 is fixedlyattached to frame member 33 by screws 36 as shown in FIG. 2. Lower tray17 is attached to the bottom of bracket 32 by screws 37, also as shownin FIG. 2.

After leaving the pool of liquid in the tray, the developed sheet Spasses between squeegee rolls 38-39 which may also serve to draw thematerial through the tray. Between the exit end of the tray and thesqueegee rolls is a V-shaped guide 40 which guides the material flatwiseinto the nip between the rolls so that the material does not tend towrinkle.

In passing through the developer station between electrodes 19 and 31the back, or non-image side, 11 of the sheet S comes into contact withthe screen electrode 31 while the image side is generally removed fromthe upper electrode so as to avoid extended pressure contact therewith,although some relatively light contact may occur without adverse effecton the developed image. It has been found in accordance with theinvention that the spacing between the upper electrode 19 and the lowerelectrode 31 should be within a range between about inch to about 1/16inch to achieve the desired improved contrast in the developed image. Inone satisfactorily used embodiment of the invention a spacing of aboutVs inch has provided excellent results. Even at such closely spacedpositions it has been found that there is little or no tendency for theimage bearing sheet to jam therebetween during its passage through thedeveloper station.

Thus, in accordance with the invention, the meshlike character of thelower electrode 31 avoids the need for dielectric ribs or guides and thelower or non-image side 41 of the image bearing sheet effectivelycontacts the electrode 31 over a relatively large area during itspassage without causing any streaking of either the back side or theimage side thereof. When a metallic screen material is used for upperelectrode 19 an effective compromise is made between the relativelycoarse mesh size needed to provide sufficient mechanical strength forshaping the electrode to form the desired concave path with minimalsupport only along its ends through frame 20 and the relatively finemesh size which is desired in order to achieve the intensified imageduring the developing process. Thus, screens having mesh sizes rangingfrom about 30 to about 325 have been found effective and in a preferredembodiment an mesh screen size has been found preferable for manypractical applications. If the mesh size is too fine it becomes moredifficult mechanically to mount the upper screen electrode so as toprovide a smooth concave path under which the sheet passes without theuse of additional more elaborate and complicated support means therefor.On the other hand, if the mesh is too coarse the contrast in thedeveloped image becomes less effective and the improvement over priorused electrodes is not nearly so noticeable.

The mesh size of the lower electrode is not as critical as that of theupper electrode and is selected so that, on the one hand, it is fineenough to produce the desired electrical characteristics and, on theother hand, not so coarse as to cause jamming of the sheet 5 in theopenings thereof, particularly as the sheet enters the developmentstructure. Generally, the mesh size should be no lower than about 10mesh, depending on the shape of the development structure, the angle ofentry thereto of the sheet S and the nature of the sheet material beingused. Further, while a relatively fine mesh can be used for the lowerelectrode, the use of mesh sizes greater than about 80 mesh may make thefabrication and installation thereof more difficult than necessary inmany practical applications, without producing any further improvementin the electrical characteristics that are desired. It has been foundthat a 30 mesh size has proved to produce satisfactory results for mostapplications.

The spacing between the upper and lower electrodes can lie within arange from about 1/16 inch up to about A inch and it has been found thatin one satisfactory embodiment of the invention good contrast can bemaintained when such spacing is about /8 inch. In using the invention inany particular application, the specific structure thereof, as selectedfor use, will normally take into account the relationships between meshsize of the upper electrode, upper and lower electrode spacing, tonerconcentration, and speed of operation.

In one successfully used embodiment excellent contrast has been achievedusing an upper screen electrode having an 80 mesh size, a lower screenelectrode having a 30 mesh size, an electrode spacing of /8 inch, andpaper speeds through the developer from about 1 to 10 inches per second.

When the metallic screen electrode 31 of the invention is utilized, thetray 17, as mentioned above, need not be made of metal as in the priordiscussed structure of the Mackenzie patent wherein the tray itself isused as the lower electrode. Consequently, the tray may be made of aplastic or other non-metallic material, for example, since it is usedmerely to form and hold an appropriate pool of developer duringoperation.

Moreover, while both the upper and lower electrodes in the embodimentshown and discussed above are metallic, in order to enhance thesmoothness of travel of a sheet therethrough, either one or bothelectrodes in some applications may be very thinly coated with a plasticmaterial, such as an epoxy resin, the thickness of which should be nogreater than about 1 mil, so that the desired electrical effect of theelectrode on the image will not be disturbed. In any event, both theupper and lower electrodes are maintained at the same potential and inthe embodiment shown in the drawing they are, in effect, electricallyconnected together through brackets 21 and 32 which are commonlyattachedto frame member 33. Frame member 33 is, in turn, connected to support15, the latter being at a suitable reference potential, such as groundpotential, for example.

While one desirable embodiment of the invention has been disclosed byway of example, it should be understood that the invention is broadlyinclusive of other modifications which may fall within the scope of theappended claims.

What is claimed is: g

1. Apparatus for developing electrostatic images on sheet materialcomprising a developer station, means for moving said sheet materialthrough said developer station, an upper electrode at said developerstation, a lower electrode at said developer station positioned oppositesaid upper electrode, said sheet material being conveyed between theelectrodes, said upper electrode and said lower electrode being ofperforated material and being equipotential members, said lowerelectrode being in contact with said moving sheet material, and thespacing between the electrodes being less than about inch.

2. Apparatus in accordance with claim 1 wherein said upper electrode ismade of metallic screen material having a mesh size in the range fromabout 30 mesh to about 325 mesh.

3. Apparatus in accordance with claim 2 wherein said electrode mesh sizeis about mesh.

4. Apparatus in accordance with claim 1 wherein said lower electrode isa metallic screen.

5. Apparatus in accordance with claim 4 wherein the screen size iswithin a range from about 10 mesh to about 80 mesh.

6. Apparatus in accordance with claim 5 wherein said mesh size is about30 mesh.

7. Apparatus in accordance with claim 1 wherein the spacing between saidelectrodes is in a range from about A. inch to about 1/16 inch.

8. Apparatus in accordance with claim 7 wherein said spacing is aboutinch.

9. Apparatus in accordance with claim 1 wherein said electrodes are atthe same electrical potential.

10. Apparatus in accordance with claim 7 wherein said electricalpotential is ground potential.

11. Apparatus in accordance with claim 1 wherein at least one of saidelectrodes is coated with a dielectric material.

12. Apparatus in accordance with claim 11 wherein both said electrodesare coated with a dielectric material.

13. Apparatus in accordance with claim 11 wherein the coating is adielectric material having a thickness of about 1 mil or less.

14. Apparatus in accordance with claim 13 wherein said dielectricmaterial is an epoxy resin.

1. Apparatus for developing electrostatic images on sheet materialcomprising a developer station, means for moving said sheet materialthrough said developer station, an upper electrode at said developerstation, a lower electrode at said developer station positioned oppositesaid upper electrode, said sheet material being conveyed between theelectrodes, said upper electrode and said lower electrode being ofperforated material and being equipotential members, said lowerelectrode being in contact with said moving sheet material, and thespacing between the electrodes being less than about 1/4 inch. 2.Apparatus in accordance with claim 1 wherein said upper electrode ismade of metallic screen material having a mesh size in the range fromabout 30 mesh to about 325 mesh.
 3. Apparatus in accordance with claim 2wherein said electrode mesh size is about 80 mesh.
 4. Apparatus inaccordance with claim 1 wherein said lower electrode is a metallicscreen.
 5. Apparatus in accordance with claim 4 wherein the screen sizeis within a range from about 10 mesh to about 80 mesh.
 6. Apparatus inaccordance with claim 5 wherein said mesh size is about 30 mesh. 7.Apparatus in accordance with claim 1 wherein the spacing between saidelectrodes is in a range from about 1/4 inch to about 1/16 inch. 8.Apparatus in accordance with claim 7 wherein said spacing is about 1/8inch.
 9. Apparatus in accordance with claim 1 wherein said electrodesare at the same electrical potential.
 10. Apparatus in accordance withclaim 7 wherein said electrical potential is ground potential. 11.Apparatus in accordance with claim 1 wherein at least one of saidelectrodes is coated with a dielectric material.
 12. Apparatus inaccordance with claim 11 wherein both said electrodes are coated with adielectric material.
 13. Apparatus in accordance with claim 11 whereinthe coating is a dielectric material having a thickness of about 1 milor less.
 14. Apparatus in accordance with claim 13 wherein saiddielectric material is an epoxy resin.